We identify the Bragg scattering process in terms of the time evolution of the correlation between the two high frequency wave amplitudes. Incorporating such effects into a wave-packet action balance and deriving a corresponding transport equation are subjects of current research. Similarly, the dynamics that control the envelope structure of the wave packet and interactions of a wave packet with the residual flow associated with the packet's envelope structure [1]} have been discarded in the ray tracing paradigm [2]}. Accounting for the latter requires loosening the specification of layer-wise constant potential vorticity [3]} which is a key piece of isopycnal coordinates representing a canonical Hamiltonian system. This, again, is a topic of current research.
